1. Technical Field
The present disclosure relates to the fabrication of integrated circuit diodes used as electrostatic discharge devices.
2. Description of the Related Art
Electrostatic discharge (ESD) occurs in a dielectric, or non-conducting, medium when an accumulation of electrostatic charge creates a voltage that exceeds the breakdown voltage of the medium. The discharge causes a sudden current to flow, dissipating the accumulated charge. Examples include a lightning discharge across an air gap, an arc between two adjacent insulated current-carrying wires, and breakdown of a capacitive structure such as a field effect transistor (FET), which includes an ultra-thin gate dielectric.
It is common for human beings to cause an ESD by simply touching an electronic device. Because integrated circuit components are so tiny, they are particularly vulnerable to damage from ESD. ESD protection devices can be deployed on board an integrated circuit chip, to protect electronic components (e.g., transistors) against static discharge events. ESD devices can incorporate diodes to block high voltages (e.g., up to about 10,000 V) and currents from reaching the electronic components, and resistors to dissipate power before it reaches the components of interest. ESD devices can also act as lightning rods to direct high currents away from the circuits to an on-board ground connection, typically established at the periphery of an integrated circuit chip. ESD devices are often located, for example, underneath bond pads, or near power supplies.
One example of an ESD device within an integrated circuit is a simple p-n junction diode that acts like a fuse. If the characteristic threshold voltage of the diode is set to be slightly smaller than the maximum voltage that can be sustained by circuit components, the diode can protect those components. When the diode threshold voltage is exceeded by a localized buildup of electrostatic charge, the diode turns on and provides a conducting path to short out the excess voltage.
Design and manufacture of effective ESD devices on board integrated circuit chips becomes increasingly challenging with each new technology generation, as device dimensions continue to shrink.